The present invention relates to antennas, and in particular, to dual-frequency patch antennas.
Patch antennas are well suited for navigation receivers in global navigation satellite systems (GNSSs). These antennas have the desirable features of compact size, light weight, and wide bandwidth. Wide bandwidth is of particular importance for navigation receivers that receive and process signals from more than one frequency band. Within a single GNSS, such as the U.S. Global Positioning System (GPS), processing signals from more than one frequency band allows certain errors to be reduced and the accuracy of coordinates to be increased. For GPS, the two primary frequency bands are the L1 band and the L2 band. For the L1 band, the mid-band frequency is approximately 1575 MHz, corresponding to a free-space (vacuum) wavelength of approximately 19 cm. For the L2 band, the mid-band frequency is approximately 1227 MHz, corresponding to a free-space wavelength of approximately 24.4 cm. In addition to GPS, the Russian GLONASS GNSS is available. Other GNSSs such as the European GALILEO system are planned. Multi-system navigation receivers (navigation receivers that can process signals from more than one GNSS) can provide higher reliability due to system redundancy and better coverage due to a line-of sight to more satellites. Multi-system navigation receivers process signals from more than one frequency band.
For GNSS applications, a dual-frequency patch antenna with compact size, light weight, and wide operational bandwidth is desirable. Other desirable properties of patch antennas for GNSS applications include a broad directional pattern in the forward hemisphere to increase the number of satellites in view, and a weak directional pattern in the backward hemisphere to reduce multipath reception.